/******************************************************
Cursor read

(c) 1997 Innobase Oy

Created 2/16/1997 Heikki Tuuri
*******************************************************/

#ifndef read0read_h
#define read0read_h

#include "univ.i"

#include "ut0byte.h"
#include "ut0lst.h"
#include "trx0trx.h"
#include "read0types.h"

/*************************************************************************
Opens a read view where exactly the transactions serialized before this
point in time are seen in the view. */

read_view_t *read_view_open_now(
    /*===============*/
    /* out, own: read view struct */
    trx_t *cr_trx,     /* in: creating transaction, or NULL */
    mem_heap_t *heap); /* in: memory heap from which allocated */
/*************************************************************************
Makes a copy of the oldest existing read view, or opens a new. The view
must be closed with ..._close. */

read_view_t *read_view_oldest_copy_or_open_new(
    /*==============================*/
    /* out, own: read view struct */
    trx_t *cr_trx,     /* in: creating transaction, or NULL */
    mem_heap_t *heap); /* in: memory heap from which allocated */
/*************************************************************************
Closes a read view. */

void read_view_close(
    /*============*/
    read_view_t *view); /* in: read view */
/*************************************************************************
Closes a consistent read view for MySQL. This function is called at an SQL
statement end if the trx isolation level is <= TRX_ISO_READ_COMMITTED. */

void read_view_close_for_mysql(
    /*======================*/
    trx_t *trx); /* in: trx which has a read view */
/*************************************************************************
Checks if a read view sees the specified transaction. */
UNIV_INLINE
ibool read_view_sees_trx_id(
    /*==================*/
    /* out: TRUE if sees */
    read_view_t *view, /* in: read view */
    dulint trx_id);    /* in: trx id */
/*************************************************************************
Prints a read view to stderr. */

void read_view_print(
    /*============*/
    read_view_t *view); /* in: read view */
/*************************************************************************
Create a consistent cursor view for mysql to be used in cursors. In this
consistent read view modifications done by the creating transaction or future
transactions are not visible. */

cursor_view_t *read_cursor_view_create_for_mysql(
    /*==============================*/
    trx_t *cr_trx); /* in: trx where cursor view is created */
/*************************************************************************
Close a given consistent cursor view for mysql and restore global read view
back to a transaction read view. */

void read_cursor_view_close_for_mysql(
    /*=============================*/
    trx_t *trx,              /* in: trx */
    cursor_view_t *curview); /* in: cursor view to be closed */
/*************************************************************************
This function sets a given consistent cursor view to a transaction
read view if given consistent cursor view is not NULL. Otherwise, function
restores a global read view to a transaction read view. */

void read_cursor_set_for_mysql(
    /*======================*/
    trx_t *trx,              /* in: transaction where cursor is set */
    cursor_view_t *curview); /* in: consistent cursor view to be set */

/* Read view lists the trx ids of those transactions for which a consistent
read should not see the modifications to the database. */

struct read_view_struct
{
  ibool can_be_too_old; /* TRUE if the system has had to purge old
                        versions which this read view should be able
                        to access: the read view can bump into the
                        DB_MISSING_HISTORY error */
  dulint low_limit_no;  /* The view does not need to see the undo
                        logs for transactions whose transaction number
                        is strictly smaller (<) than this value: they
                        can be removed in purge if not needed by other
                        views */
  dulint low_limit_id;  /* The read should not see any transaction
                        with trx id >= this value */
  dulint up_limit_id;   /* The read should see all trx ids which
                        are strictly smaller (<) than this value */
  ulint n_trx_ids;      /* Number of cells in the trx_ids array */
  dulint *trx_ids;      /* Additional trx ids which the read should
                        not see: typically, these are the active
                        transactions at the time when the read is
                        serialized, except the reading transaction
                        itself; the trx ids in this array are in a
                        descending order */
  trx_t *creator;       /* Pointer to the creating transaction, or
                        NULL if used in purge */
  UT_LIST_NODE_T(read_view_t) view_list;
  /* List of read views in trx_sys */
};

/* Implement InnoDB framework to support consistent read views in
cursors. This struct holds both heap where consistent read view
is allocated and pointer to a read view. */

struct cursor_view_struct
{
  mem_heap_t *heap;
  /* Memory heap for the cursor view */
  read_view_t *read_view;
  /* Consistent read view of the cursor*/
  ulint n_mysql_tables_in_use;
  /* number of Innobase tables used in the
    processing of this cursor */
};

#ifndef UNIV_NONINL
#include "read0read.ic"
#endif

#endif
